The present invention relates to a method for producing a body structure composed of a stiffened panel of a fiber-reinforced composite, and a body structure produced by the method.
Fiber-reinforced composites (prepregs) are light in weight and high in strength to have been widely used for automobiles, ships, aircrafts, etc. Although most of conventional aircrafts made of the fiber-reinforced composites have a body structure composed of honeycomb sandwich panels, the body structure is preferably composed of integrally formed, stiffened panels to obtain a lighter aircraft with improved reliability. The stiffened panel, in particular, such that a skin and stiffeners are integrally formed, is the most suitable for production of lightened body structure.
FIG. 1 is a partial, schematic perspective view showing an example of the body structure composed of the stiffened panel. The body structure 1 shown in FIG. 1 comprises a skin 2, shorter stringers 3 placed in lengthening direction, and taller frames 4 placed in circumferential direction. The stringers 3 and the frames 4 are simply shown in a quadrangular prism shape, they often having a section of C-shape, I-shape, J-shape, T-shape, etc. in practical. Such a body structure is generally produced by the steps of: placing a skin member and stiffener members (preformed stringer members and preformed frame members) made of a fiber-reinforced composite on a forming tool; and adhesive-forming them by heating under a pressure using a pressure bag, etc.
Intersections of the preformed stringer members and the preformed frame members are appropriately worked. As shown in FIG. 2, a body structure for a large aircraft is generally obtained by providing an open hole 51 in a preformed frame member 41, and by making a preformed stringer member 31 pass through the open hole 51 on a skin member 21. However, providing such an open hole increases production cost of the body structure. Particularly, in the case of a body structure for a small aircraft, height of the preformed frame member is approximately 50 mm to secure a desired interior space in contrast with the large aircraft having a frame height of approximately 100 mm, so that it is difficult to provide the open hole in the preformed frame member, thereby increasing the production cost.
An object of the present invention is to provide a method for steadily producing a body structure composed of a stiffened panel of a fiber-reinforced composite with superior quality and reduced production cost, and a body structure produced thereby.
As a result of intensive research in view of the above object, the inventor has found that a body structure of superior quality can be produced with reduced production cost if a frame member is divided into an outer frame member and an inner frame member, the outer frame member being integrally formed with a skin member and a stringer member to prepare an assembly, and the inner frame member being adhesive-formed with the assembly. The present invention has been accomplished by the finding.
Thus, in a method for producing a body structure of a fiber-reinforced composite according to the present invention, a skin member, a plurality of preformed stringer members, a plurality of preformed outer frame members and an inner frame member each made of a fiber-reinforced composite are used, and (a) the skin member is placed on a forming tool, (b) the preformed stringer members are arranged on the skin member at predetermined intervals, (c) the preformed outer frame members are arranged on the skin member to intersect the preformed stringer members, (d) the skin member, the preformed stringer members and the preformed outer frame members are integrally hardened by heating under a pressure to prepare an assembly having a skin, stringers and an outer frame, (e) the inner frame member hardened by heating under a pressure beforehand is put into contact with the outer frame, and (f) the inner frame member and the assembly are adhesive-formed by heating under a pressure.
In the method of the present invention, the preformed stringer members pass through spaces between the preformed outer frame members and the inner frame member, so that there is no need to provide the above-described open hole. Further, dimensional error of the preformed outer frame members and the inner frame member can be absorbed when they are adhesive-formed, whereby a body structure excellent in dimensional accuracy can be produced with high reliability.
The preformed outer frame members preferably have a T-shaped section, and the inner frame member preferably has an L-shaped section. The L-shaped inner frame member can be formed and placed easier than a member of C-shape, J-shape, etc., thereby reducing production cost and steadying quality of the body structure. Further, it is preferred that the inner frame member is a seamless ring in shape from the viewpoint of strength of the body structure.
The inner frame member is preferably hardened by heating at 120 to 250xc2x0 C. under a pressure beforehand, the skin member, the preformed stringer members and the preformed outer frame members are preferably integrally hardened by heating at 120 to 250xc2x0 C. under a pressure, and the inner frame member and the assembly are preferably adhesive-formed by heating at 120 to 180xc2x0 C. under a pressure.
A body structure of the present invention can be produced by the method according to the present invention mentioned above.